Why is my dog's pupil suddenly pinhole size in one eye? Vet needed?

Yes, that is definitely something you should be worried about. What you are seeing is called anisocoria, and when it suddenly appears, it is a medical emergency. This can be due to corneal injury, disease or injury to the brain, disease or injury to the nerves running to the eye, or uveitis among other causes. I would take Ace into an ER vet or find a vet on call to see him ASAP to diagnose what is causing the anisocoria so it can be treated.

Hi there! Thanks for using Petco Pet Education Center, formerly Petcoach! This could have been due to some degree of mild trauma. If she is otherwise doing well, and the size of the pupils normalize in the next 24-48 hours, then she is likely to be just fine. If no improvement is noted or she worsens, then have her evaluated by your veterinarian for further assessment and treatment. Good luck with your girl!

This can be a sign of an eye problem - the eye can dilate if a toxin has been ingested, or it's possible that the other pupil is actually constricted secondary to pain or a scratch on the eye. I'd recommend seeing your veterinarian for an exam of the eyes. If Nova seems to be painful or disoriented I"d recommend seeing an emergency veterinarian today.

The pupil can constrict with bleeding or inflammation in the anterior chamber of the eye, blunt trauma, or a scratch to the surface of the eye. If you see blood, if your dog is squinting or seems painful, or if there is discharge from the eye I’d recommend traveling to see an emergency vet if at all possible since some conditions could compromise vision if left untreated. Otherwise I think you could monitor her for a day but if the pupil does not return to normal within 24 hours I’d recommend seeing a vet.

Hello and thank you for contacting Petco Pet Education Center, formerly Petcoach. Oso definitely should be fully checked by your local vet. Difference in pupils size can be caused by ocular trauma (for example blunt trauma to the eye when Oso hit the bench) or less frequently, by brain concussion / brain trauma. Your vet will be able to distinguish between these two problems and recommend treatment, if required.

Pupils will change in size frequently depending on the amount of light and other stimuli. Also, the right and left pupils can be different sizes at the same time. You should check Blaze's eye in about 30 minutes to make sure that the pupil has returned to normal size. You may want to do this in a dimly lit room since this will make the pupil bigger. Do not shine a light into his eye since the pupil with automatically contract and become smaller. If his pupil is bigger and is changing in size, you do probably do not need to be concerned. You should also watch Blaze's eye over the next day or so for any redness or swelling. If you notice any of these signs you should take Blaze to your veterunarian.

This is a medical condition called [anisocoria](https://www.tuftsyourdog.com/doghealthandmedicine/dog-has-different-sized-pupils/) - most of the time, it indicates either a neurological problem or an injury to one of [the eyes](https://www.petcoach.co/article/sight-development-in-the-dog-puppy). However, occasionally in some puppies this condition may occur intermittently with no obvious cause and no other symptoms associated with it - the cause is as yet unknown, but the puppies are otherwise perfectly normal. If this is the first time you have noticed this, I would recommend taking Tucker to a veterinarian or [veterinary ophthalmologist ](https://www.acvo.org/)for an exam to be on the safe side - he may have an eye or head injury, some type of neurological disease, or been exposed to something toxic that could cause this. If his exam is completely normal and he shows no other symptoms, then in the future you could choose to simply monitor at home for other problems.